Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$43.94	6.495%	$46.7939	$46.79	$46.80	$46.80
Purchase #2	$70.54	6.716%	$75.2775	$75.28	$75.30	$75.30
Purchase #3	$55.40	11.172%	$61.5893	$61.59	$61.60	$61.60
Purchase #4	$232.74	9.298%	$254.3802	$254.38	$254.40	$254.40
Purchase #5	$170.32	9.109%	$185.8344	$185.83	$185.85	$185.80
Purchase #6	$101.32	6.570%	$107.9767	$107.98	$108.00	$108.00
Purchase #7	$178.89	12.153%	$200.6305	$200.63	$200.65	$200.60
7 purchase totals =	$853.15		$932.4825	$932.48	$932.60	$932.50